Earthquake in Switzerland

A series of violent earth tremors reduced the city of Basel to rubble on 18 October 1356. From the afternoon until midnight, the earth trembled again and again. Many houses and part of Basel Cathedral collapsed. The quake and the subsequent fire razed the city to the ground. It is not yet known exactly how many victims there were.

It is the worst natural disaster in the history of Switzerland. At around four o’clock in the afternoon, the first earth tremor caused numerous houses and the choir of Basel Cathedral to collapse. Many of the inhabitants of Basel were seized by panic and fled to the fields outside the city gates. The flight was their salvation. For in the late evening, strong tremors followed again, which could still be felt at a distance of 50 kilometres. Even the strongest walls collapsed.

To make matters worse, the city began to burn: Fireplaces and candles in the collapsing buildings caused fires to break out several times. What the earthquake had not destroyed was destroyed by the fire, which raged for a whole eight days after the quake. When the flames finally died down, the cathedral and many churches and monasteries were badly damaged. Not even a hundred houses remained standing; most of the buildings are in ruins. The number of dead is currently estimated at 300. Many survivors no longer have a home. They now live in makeshift tents outside the city gates.

Help from the neighbourhood

Many people in Basel have lost everything due to the earthquake and fire. They lack the most basic necessities, especially food. The rural population in the surrounding area is very helpful, providing food and drink to those affected. Cities further away, such as Strasbourg, Freiburg and Colmar, also offer their support. They are sending helpers with tools and horse-drawn carts to help clear alleys and rebuild houses. Donations have also been pledged. As soon as possible, the long-suffering city of Basel and its cathedral should be back as it was before the great earthquake.

Upper Rhine Graben

Doors rattle without the slightest wind blowing. Cups clatter in the cupboard as if moved by a ghostly hand. This is not a scary movie, but reality in the Upper Rhine Graben. In this region in southwest Germany, there are smaller earthquakes every few months. This is surprising, because there is no plate boundary to be seen here, far and wide.

The Upper Rhine Graben is a depression about 300 kilometres long and up to 40 kilometres wide between Basel and Frankfurt. At first it looks like an ordinary river valley, but it owes its formation to a weak point in the earth’s crust.

Along this weak spot, a trench collapsed in the course of the last 45 million years. In the process, the sinking rock disintegrated into fragments of different sizes and partially slid down into the trench. At the same time as the trench sank, the rock was lifted at its edges. This is how the “trench shoulders” developed, which can still be recognised today as the Black Forest and the Vosges. However, the erosion constantly compensated for the difference in height between the depression and the mountains: Debris and rock slabs slid in from the sides and filled up the trench again and again. Thick sediment layers accumulated at its bottom, through which the Rhine only found its way much later.

To this day, the earth’s crust is expanding and moving in the area of the Upper Rhine Graben. The trench sinks almost one millimetre every year. Thus, tensions are constantly building up in the rock, which are repeatedly discharged in smaller earthquakes. One earthquake, however, was unusually violent and reduced the city of Basel to rubble in 1356.

Whether such a strong quake could happen again soon is difficult to answer, even for experts. The processes in the earth’s crust are still far from being completely understood. There are several possible explanations for the formation of the rift: one cause could be that the African plate is pressing against the European plate from the south. In the process, the Alps were folded up and presumably also the Black Forest and the Vosges were lifted. The enormous pressures and tensions could have caused the rock of these older mountains to break apart, thus creating the rift valley. Another assumption is that magma from the Earth’s mantle pushed upwards, stretched the Earth’s crust and thus ripped open the trench. To find out exactly what happened, the Upper Rhine Graben is still monitored and studied by geologists today.

When the earth shakes

The earth trembles, cracks gape in the ground, trees sway and houses collapse – earthquakes are natural forces with destructive power. When the earth shakes, entire city districts can collapse. In certain areas, the earth shakes particularly often, namely where the plates of the earth’s crust adjoin each other. This is the case, for example, in Japan, on the west coast of the USA or in the Mediterranean region.

The cause of earthquakes is the movement of the plates. They float on the viscous material of the earth’s mantle, whose currents drive them like an engine. Where two plates border on each other, their rock masses can get caught and stalled. The problem is: the currents in the Earth’s interior continue to drive them. This creates enormous tensions between the two plates. If the tensions become too great at some point, one of the plates jerks forward. The tension discharges: the earth shakes.

Earthquakes often happen where two plates slide past each other at different speeds, like on the coast of California. Where plates collide, this does not happen smoothly either. For example, the African plate drifts towards the Eurasian plate and dives under it. Because this plate boundary runs through the Mediterranean region, the earth shakes again and again in Italy and Turkey. Earth tremors also occur where the earth’s crust is being torn apart, for example in the Upper Rhine Graben. Although these have been less severe in past centuries, there have also been violent tremors here: In 1356, a strong quake caused great damage in the city of Basel.

Not every time is the movement of the plates “to blame” for an earthquake. Collapses can also shake the environment. This happens when natural or man-made cavities collapse. However, such quakes do not reach as far and are not as strong as quakes triggered by the movement of the earth’s plates.

The exact point from which an earthquake originates is the earthquake focus, also called the hypocentre. From here, the earthquake waves spread out in all directions – comparable to the waves after a stone has plunged into the water. The greater the distance from the earthquake focus, the weaker the earthquake waves that cause the earth to sway.

Continents on the move

For a long time, it was thought that the earth’s land masses stood rigidly in place. Later it turned out: the opposite is the case. The continents of our planet are moving! Like huge ice floes, they drift in different directions, albeit not very fast. Their speed is about the same as the growth of a fingernail. But why are the continents constantly on the move?

The earth’s crust that envelops our planet is brittle and cracked. It resembles a cracked eggshell and is made up of seven large plates and many smaller ones. Some of them form the continents, others the ocean floor. These plates of the Earth’s crust drift around on a hot, viscously flowing mush of rock and are driven by movements in the Earth’s interior, or more precisely: by currents in the Earth’s mantle. Experts also say: they drift. All these processes surrounding the movement of the Earth’s plates are called plate tectonics, and the movement itself is also called plate drift.

Where the individual plates border on each other, the Earth is particularly active. At some of these plate boundaries, hot rock from the Earth’s mantle penetrates upwards and cools down. New crust forms here: the two plates grow and are pushed apart as a result. In contrast, where two plates collide, the lighter of the two – the continental crust – is crumpled and folded into mountains. The heavier of the two – the oceanic crust – slowly disappears into the depths. The heat in the Earth’s interior melts its rock again. While the edge of the plate sinks into the depths, it pulls the rest of the plate behind it and thus additionally drives the plate movement.

Volcanic eruptions, earthquakes, long mountain ranges and deep ocean trenches accumulate along such plate margins. Most of the turmoil on the Earth’s surface is caused by the largest of its plates: it is the Pacific Plate, which is moving northwest at a rate of about 10 centimetres per year. Most of the earth’s active volcanoes are found at its edges, and violent earthquakes shake the region. Because of the frequent volcanic eruptions and quakes, this plate boundary is also called the “Pacific Ring of Fire”.

The outermost shell of the earth

Like an egg from an eggshell, the Earth is also surrounded by a hard shell. This outermost layer surrounds the Earth’s mantle and is called the Earth’s crust. If you compare the earth to a peach, the earth’s crust is – relatively speaking – as thick as its skin. Under continents, it reaches an average depth of 40 kilometres, under the oceans even only about seven kilometres.

Below this lies the outer part of the Earth’s mantle, which reaches down to a depth of about 100 kilometres. It is also solid, but consists of heavier rock. The earth’s crust and this outermost part of the mantle together are also called the “lithosphere”. This solid layer of rock is broken into plates of different sizes that drift very slowly on the hot, viscous mantle.

Where the molten rock from the hot mantle penetrates upwards, the earth’s crust can break open. Lava then flows out and becomes new crust. This mainly happens where the plates of the lithosphere adjoin each other, such as at the mid-ocean ridges.

The crust is covered by the soil. The soil of the land masses forms from weathered rock and the remains of animals and plants. The seabed, on the other hand, develops from deposits such as clay and the sunken remains of marine organisms. On the coasts, the seabed also consists of deposited debris that has been eroded from the mainland and washed into the sea.

Tension grows in California

No state in the USA is more densely populated than California. Los Angeles alone has almost four million inhabitants. And this despite the fact that the region is on extremely shaky ground: California is an earthquake zone. At some point, the earth will shake violently here again. Experts warn that the time could come soon. Is the big quake – “The Big One” – imminent?

For many years it has been remarkably quiet in California. Too quiet, some fear. True, there are smaller quakes all the time and many of them are so weak that they are not noticeable. But the last big quake happened 100 years ago: In April 1906, it destroyed San Francisco. The reason for the increased earthquake danger is that a large rift runs lengthwise through California: At the San Andreas Fault, two plates of the earth’s crust meet. If their rock masses move jerkily, the earth’s surface cracks violently. And the tension at the edges of the plates grows daily.

Geologists have calculated that a destructive earthquake with a magnitude of more than 6.7 is very likely in the next 20 to 30 years. According to experts, the question is not if the catastrophe will come, but when. Californians seem to be taking the tension in the rock calmly. Although the skyscrapers are earthquake-proof, many older buildings are not. Whether the nuclear power plants are safe enough is uncertain. And every now and then, radio stations and newspapers encourage the population to have the bare essentials in the house for the worst case scenario: food, drink and cash.

The Great San Francisco Quake

It was 100 years ago, but the inhabitants of California still have terrible memories of the day: In the early morning hours of 18 April 1906, the earth began to shake violently in San Francisco and the surrounding area. The main quake lasted only about 40 seconds, but the consequences were fatal. Whole quarters of the burgeoning city collapsed. Fires broke out in many parts of the city, adding to the scale of the disaster. It is not certain how many people died in the earthquake. Officially, the death toll is 3000, and thousands more were left homeless. There were also many victims and destruction in the San Francisco area. Property damage was in the tens of millions of dollars. The quake hit California completely unexpectedly. No one had expected such a catastrophe at the time.

Tsunami disaster in Japan

The seaquake that shook the seabed off the coast of Japan on Friday, 11 March 2011, has had devastating consequences. The quake triggered a tsunami more than 10 metres high, which rushed towards the coast at several 100 kilometres per hour. The water flooded a 1000-kilometre-long coastal strip and left a picture of devastation. It is not yet known how many people died in the disaster. The monster waves also hit the Fukushima nuclear power plant and destroyed its cooling system. Explosions at the reactor blocks raise fears of a core meltdown.

With a magnitude of 8.9, it was the worst earthquake in Japan’s history. It began at 2.45 p.m. local time, its epicentre was 130 kilometres east of the city of Sendai in the north-east of the country. A tsunami more than ten metres high swept over the coast of the Japanese main island of Honshu a few minutes later. The powerful tidal wave hurled ships inland, swept buildings away and buried the coastal strip under a layer of mud. Tens of thousands of people were victims of the floods, countless are missing. Emergency shelters are completely overcrowded. 100,000 soldiers are now helping with the clean-up.

At the same time, fear of a super-GAU is growing in Japan. At the Fukushima nuclear power plant, the cooling system for the fuel rods has failed. It is possible that the meltdown has already begun. The government has declared a nuclear state of emergency. Thousands of residents have been evacuated in the meantime.

Tsunami warning for Europe?

Even Europe is not safe from a tsunami. The Mediterranean region is tectonically active and earthquakes are the result. After particularly strong seaquakes, the feared giant waves could therefore pile up in the Mediterranean and even in the Atlantic. This already happened about 2000 years ago, when a quake off Crete was followed by a tsunami that devastated the coasts of the eastern Mediterranean. In 1755, a quake off Portugal and the subsequent tsunami destroyed the city of Lisbon. And a quake off Sicily also caused a giant wave in 1908. Because people are now more aware of these dangers again, experts are now working on a tsunami early warning system for Europe.

Bold theory: the earth’s parts are moving!

During a conference of the Geological Society in Frankfurt, the meteorologist and polar researcher Alfred Wegener put forward a daring theory: According to him, the continents move around the earth. Colleagues in geology expressed scepticism to the point of rejection.

If Alfred Wegener had claimed that the Earth was a disc, he would hardly have caused any more astonishment among his listeners. According to Wegener, all the continents of our earth were united into a single land mass a long time ago. He calls this supercontinent Pangaea, which moved along the Earth’s mantle and broke into two parts 200 million years ago. These two parts of the earth are said to have continued to divide and shift. There are clear indications of the break-up and movement of the continents: they fit into each other like pieces of a jigsaw puzzle. It is also striking that the same animal species occur on different continents.

So Africa and South America should have been one? For the experts, Wegener’s speech sounds as credible as a fairy tale from the Arabian Nights. After all, to this day we are convinced that the earth’s crust is firmly connected to its subsoil. According to current knowledge, the continents are fixed and were once connected to each other via land bridges. Many geologists still disparagingly refer to Wegener’s continental drift as the “geopoetry of a weatherman”. For what remains unexplained is above all the motor of the movement: What is driving the continents? But research can no longer ignore Alfred Wegener’s theory. Can it be proven?

Alfred Wegener – an airhead?

The meteorologist Alfred Wegener became famous for a record he set in balloon flight: On 5 April 1906, he ascended together with his brother Kurt and stayed in the air for over 52 hours. This beat the previous world record by 17 hours. But the balloon flight was not only for fame, but above all for science: the Wegener brothers wanted to explore the atmosphere and test methods for determining locations. Alfred Wegener’s interest was not only in the weather and aviation, however, but also in the eternal ice. In the very year of his world record, he set out to explore Greenland. He returned from this Greenland expedition in 1908. Since then, the 32-year-old natural scientist has been a lecturer in meteorology, astronomy and physics at the University of Marburg.